The present invention relates to vibration damping materials comprising a polymer. The invention further relates to data storage medium prepared from the high glass transition temperature vibration damping materials.
Vibration damping is a common need in many mechanical systems where undesired resonances may be excited by normal perturbations. The suspension system in an automobile, for example, will exhibit large unwanted oscillations in response to road irregularities unless properly damped. Vibration dampers used in automobiles consist of springs providing shock and vibration isolation to a motor vehicle seat assembly.
Layers of elastomeric materials that absorb energy are other types of damping material. Polyethylene, polypropylene. non-conjugated dienes, rubber cross linkers and similar materials are used in these vibration systems. Composites of metal and polymer are employed on the outside of many computer hard disk drives to reduce the noise of the drive within the computer. Vibration dampers are also used in printed circuit boards and spindle motors in internal disk drive applications. In particular, vibration damping materials are used to guard the interior of a disk drive from external shock forces.
Due to a wide range of possible applications, there has been an intense research in polymer systems capable of damping out vibrations. Most polymer systems have a low fundamental vibration frequency. Many of these systems employ an elastomer in combination with a glassy polymer, metal, or combination thereof which are in contrast to single phase homogenous materials, i.e. monolithic systems. Monolithic polymers have the advantage of better surface smoothness. Thus, it would be desirable to develop damping systems which offer damping at room temperature without the use of a dispersed rubbery phase or blocky copolymer. xe2x80x9cBlocky copolymerxe2x80x9d as used herein refers to multiple phase polymer systems with alternating monomer sequences that may be of varying length.
One area in which there has been intense research in polymer systems capable of damping out vibrations is in xe2x80x9cfirst surfacexe2x80x9d media. Unlike compact discs and digital video disks (DVD), storage medium having high areal density capabilities, typically greater than 5 Gigabits per square inch, employ first surface or near field read/write techniques in order to increase the areal density. xe2x80x9cFirst surfacexe2x80x9d as used herein refers to the data layer which is on the surface of a substrate wherein an optic does not pass through the substrate. xe2x80x9cNear field read/write techniquesxe2x80x9d as used herein refers to an optical mechanism wherein the numericai aperture is greater than about 1. For such storage media, although the optical properties are not relevant, the physical and mechanical properties of the substrate become increasingly important. For high areal density applications, including first surface applications, the surface quality of the storage medium can affect the accuracy of the reading device, the ability to store data, and replication qualitites of the substrate. Furthermore, the physical characteristics of the storage medium when in use can also affect the ability to store and retrieve data. For instance, if the axial displacement of the medium is too great, the axial displacement can inhibit the accurate retrieval of data and/or damage the read/write device. Thus, improved vibration performance may be achieved by either high modulus or high damping.
In addition to high damping, the storage medium should be capable of withstanding subsequent processing parameters, for example, application of subsequent layers such as sputtering (i.e. temperatures up to and exceeding about 200xc2x0 C., typically up to or exceeding about 300xc2x0 C.) for magnetic media, and temperatures of about 25xc2x0 C. up to about 150xc2x0 C. for magneto-optic media.
In the hard disk industry standard Cobalt-Chromium-Platinum (CoCrPt) longitudinal recording alloys are predominantly utilized as the sputtered medium. In the sputtering process the high substrate temperatures serve a few purposes. First, it tends to lead to lower-noise films. It is speculated that temperature promotes compositional segregation of grains by promoting the diffusion of chromium to grain boundaries. Lower noise films directly translate to the ability to support higher density recording by allowing one to maintain an acceptable signal to noise (S/N) with decreasing signal. The second major influence is that for these types of alloys, higher temperature (among other factors) tends to promote higher film coercivity. Higher coercivity promotes improved thermal stability and thus improves performance. Thus, it is desirable for the storage medium to have sufficient thermal stability to prevent deformation during the deposition steps.
Vibration concerns and thermal stability are critical in the design of data storage devices, such as optical disk drives and hard disk drives. Thus, there is a need to develop damping systems utilizing polymers which are suitable for use in data storage devices, in particular in substrate applications.
The present invention provides a storage medium for data, the storage medium comprising:
1) a substrate comprising at least one polycarbonate portion, and
2) at least one data layer on the substrate;
the polycarbonate comprising at least one compound of structure, (I), (II), (III), or (IV): 
wherein the polycarbonate has a glass transition temperature of at least about 150xc2x0 C.
The present invention further provides a polycarbonate composition comprising at least one compound of structure (I), (II), (III), (IV), or combinations thereof wherein the polycarbonate has a mechanical damping coefficient greater than about 0.04 at a temperature about 24xc2x0 C. and a glass transition temperature greater than about 150xc2x0 C.
The present invention further provides a method for improving the damping performance of an article, the method comprising constructing the article of a polycarbonate with at least one compound of structure (I), (II), (III), (IV), or combinations thereof wherein the polycarbonate has a mechanical damping coefficient greater than about 0.04 at a temperature about 24xc2x0 C. and a glass transition temperature greater than about 150xc2x0 C.